Conventionally, in a rotary working machine such as a power shovel, a rotation table frame is generally arranged on a traveling device; a working machine including a boom and arm as well as an attachment such as a bucket is supported in a front and back rotatable manner at the front part of the rotation table frame; and an engine, a radiator, and the like are arranged at the rear part of the rotation table frame while being covered by the bonnet.
A cooling fan and a radiator are arranged on the side of the engine in the bonnet where the cooling airflow produced by the cooling fan cools the engine and thereafter passes through the radiator as discharge airflow and is discharged to the side of the main equipment through an opening formed on the side surface of the bonnet. An airflow direction plate is arranged in the opening or in a duct arranged between the radiator and the opening so that the airflow direction of the discharge airflow can be changed in the up and down direction (see e.g., Patent Document 1).
However, in the rotary working machine in the prior art, since the airflow direction of the discharge airflow discharged from the opening on the side surface of the bonnet is fixed in a constant up and down direction, the discharge airflow that has become hot airflow might blow against trees positioned to the side of the main equipment or on walkers walking near the side of the main equipment depending on the situation of the working place. Furthermore, a drawback in that the discharge airflow blows against the operator himself/herself who is on the main equipment may arise due to change in the airflow direction.    [Patent Document 1] Japanese Laid-Open Patent Publication No. 2004-352089